Method and apparatus for printing images from digital image data

ABSTRACT

An apparatus for printing images from digital image data onto a light sensitive medium disposed at an image plane which comprises a control logic processor capable of controlling the operation of the apparatus for printing based on the digital image data. An image forming assembly directs an exposure beam to the light sensitive medium disposed at the image plane. The image forming assembly ( 10 ) comprises a light source, a first lens assembly ( 41 ), a beamsplitter ( 50 ), a spatial light modulator ( 52 ), a temperature profile control apparatus ( 51 ) and a second lens assembly ( 132 ).

CROSS REFERENCE TO RELATED APPLICATIONS FIELD OF THE INVENTION

This invention relates generally to a printing apparatus and method forimaging onto photosensitive media by modulating a light beam, and moreparticularly to a film recording apparatus wherein a temperature profileof a spatial light modulator is controlled.

BACKGROUND OF THE INVENTION

Conventional printers generally adapted to record images provided fromdigital data onto photosensitive media apply light exposure energy thatmay originate from a number of different sources and may be modulated ina number of different ways. In photoprocessing apparatus, for example,light exposure energy can be applied from a CRT printer. In a CRTprinter, the digital data is used to modulate a cathode ray tube (CRT)which provides exposure energy by scanning an electron beam of variableintensity along its phosphorescent screen. Alternately, light exposureenergy can be applied from a laser printer, as is disclosed in U.S. Pat.No. 4,728,965 (Kessler et al.) In a laser-based printer, the digitaldata is used to modulate the duration of laser on-time or intensity asthe beam is scanned by a rotating polygon onto the imaging plane.

CRT and laser printers perform satisfactorily for photoprocessingapplications, that is, for printing of photographs for consumer andcommercial markets. However, in an effort to reduce cost and complexity,alternative technologies have been considered for use in photoprocessingprinters. Among suitable candidate technologies under development aretwo-dimensional spatial light modulators.

Two-dimensional spatial light modulators, such as those using a digitalmicromirror device (DMD) from Texas Instruments, Dallas, Tex., or usinga liquid crystal device (LCD) can be used to modulate an incomingoptical beam for imaging. A spatial light modulator can be consideredessentially as a two-dimensional array of light-valve elements, eachelement corresponding to an image pixel. Each array element isseparately addressable and digitally controlled to modulate incidentlight from a light source by, for instance, in the case of a LCDmodulator, modulating the polarization state of the light. Polarizationconsiderations are, therefore, important in the overall design ofsupport optics for a spatial light modulator.

There are two basic types of spatial light modulators in current use.The first type developed was the transmissive spatial light modulator,which, as its name implies, operates by modulating an optical beam thatis transmitted through individual array elements. The second type, alater development, is a reflective spatial light modulator. As its nameimplies, the reflective spatial light modulator operates by modulating areflected optical beam through individual array elements. A suitableexample of an LCD reflective spatial light modulator relevant to thisapplication utilizes an integrated CMOS backplane, allowing a smallfootprint and improved uniformity characteristics.

Conventionally, LCD spatial light modulators have been developed andemployed for digital projection systems for image display, such as isdisclosed in U.S. Pat. No. 5,325,137 (Konno et al.) and in miniaturizedimage display apparatus suitable for mounting within a helmet orsupported by eyeglasses, as is disclosed in U.S. Pat. No. 5,808,800(Handschy et al.) LCD projector and display designs in use typicallyemploy one or more spatial light modulators, such as using one for eachof the primary colors, as is disclosed in U.S. Pat. No. 5,743,610(Yajima et al.).

It is instructive to note that imaging requirements for projector anddisplay use (as is typified in U.S. Pat. Nos. 5,325,137; 5,808,800; and5,743,610) differ significantly from imaging requirements for printing.Projectors are optimized to provide maximum luminous flux to a screen,with secondary emphasis placed on characteristics important in printing,such as contrast and resolution. Optical systems for projector anddisplay applications are designed for the response of the human eye,which, when viewing a display, is relatively insensitive to imageartifacts and aberrations and to image non-uniformity, since thedisplayed image is continually refreshed and is viewed from a distance.However, when viewing printed output from a high-resolution printingsystem, the human eye is not nearly as “forgiving” to artifacts andaberrations and to non-uniformity, since irregularities in opticalresponse are more readily visible and objectionable on printed output.For this reason, there can be considerable complexity in optical systemsfor providing a uniform exposure energy for printing. Even moresignificant are differences in resolution requirements. Adapted for thehuman eye, projection and display systems are optimized for viewing attypical resolutions such as 72 dpi or less, for example. Photographicprinting apparatus, on the other hand, must achieve much higherresolution, particularly apparatus designed for micrographicsapplications, which can be expected to provide 8,000 dpi for somesystems. Thus, while LCD spatial light modulators can be used in a rangeof imaging applications from projection and display to high-resolutionprinting, the requirements on supporting optics can vary significantly.

Largely because spatial light modulators can offer significantadvantages in cost and size, these devices have been proposed fordifferent printing systems, from line printing systems such as theprinter depicted in U.S. Pat. No. 5,521,748 (Sarraf), to area printingsystems such as the system described in U.S. Pat. No. 5,652,661(Gallipeau et al.) One approach, using a Texas Instruments DMD as shownin U.S. Pat. No. 5,461,411 (Florence et al.) offers advantages common tospatial light modulator printing such as longer exposure times usinglight emitting diodes as a source as shown in U.S. Pat. No. 5,504,514(Nelson). However, DMD technology is very specific and not widelyavailable. As a result, DMDs may be expensive and not easily scaleableto higher resolution requirements. The currently available resolutionusing DMDs is not sufficient for all printing needs. Furthermore, thereis no clear technology path to increased resolution with DMDs.

A preferred approach for photoprocessing printers uses an LCD spatiallight modulator. Liquid crystal modulators can be a low cost solutionfor applications requiring spatial light modulators. Photographicprinters using commonly available LCD technology are disclosed in U.S.Pat. Nos. 5,652,661; 5,701,185 (Reiss et al.); and U.S. Pat. No.5,745,156 (Federico et al.) Although the present application primarilyaddresses use of LCD spatial light modulators, references to LCD in thesubsequent description can be generalized, for the most part, to othertypes of spatial light modulators, such as the DMD noted above.

Primarily because of their early development for and association withscreen projection of digital images, spatial light modulators havelargely been adapted for continuous tone (contone) color imagingapplications. Unlike other digital printing devices, such as the CRT andlaser-based devices mentioned above that scan a beam in atwo-dimensional pattern, spatial light modulators image one completeframe at a time. Using an LCD, the total exposure duration and overallexposure energy supplied for a frame can be varied as necessary in orderto achieve the desired image density and to control media reciprocitycharacteristics. Advantageously, for photoprocessing applications, thecapability for timing and intensity control of each individual pixelallows an LCD printer to provide grayscale imaging.

Most printer designs using LCD technology employ the LCD as atransmissive spatial light modulator, such as is disclosed in U.S. Pat.Nos. 5,652,661 and 5,701,185. However, the improved size and performancecharacteristics of reflective LCD arrays have made this technology adesirable alternative for conventional color photographic printing, asis disclosed in U.S. Pat. No. 6,215,547 (Ramanujan et al.) As isdescribed in U.S. Pat. No. 6,215,547, color photographic printingrequires multiple color light sources applied in sequential fashion. Thesupporting illumination optics are required to handle broadband lightsources, including use of a broadband beamsplitter cube. The opticssystem for such a printer must provide telecentric illumination forcolor printing applications. In summary, in the evolution ofphotoprocessing systems for film printing, as outlined above, it can beseen that the contone imaging requirements for color imaging aresuitably met by employing LCD spatial light modulators as a solution.

Printing systems for micrographics or computer output microfilm (COM)imaging, diagnostic imaging, and other specialized monochrome imagingapplications present a number of unique challenges for optical systems.In the COM environment, images are archived for long-term storage andretrievability. Unlike conventional color photographic images, microfilmarchives, for example, are intended to last for hundreds of years insome environments. This archival requirement has, in turn, driven anumber of related requirements for image quality. For image reproductionquality, for example, one of the key expectations for micrographicsapplications is that all images stored on archival media will be writtenas high-contrast black and white images. Color film is not used as amedium for COM applications since it degrades much too quickly forarchive purposes and is not capable of providing the needed resolution.Grayscale representation, meanwhile, has not been available forconventional micrographics printers. Certainly, bitonal representationis appropriate for storage of alphanumeric characters and for standardtypes of line drawings such as those used in engineering and utilitiesenvironments, for example. In order to record bitonal images ontophotosensitive media, exposure energy applied by the printer is eitheron or off, to create high-contrast images without intermediate levels orgrayscale representation.

In addition to the requirement for superb contrast is the requirementfor high resolution of COM output. COM images, for example, areroutinely printed onto media at reductions of 40× or more. Overall,micrographics media is designed to provide much higher resolution thanconventional dye-based media provides for color photographic imaging. Toprovide high resolution, micrographics media employs a much smaller AgXgrain size in its photosensitive emulsion. Optics components for COMsystems are correspondingly designed to maximize resolution, more sothan with optical components designed for conventional colorphotoprocessing apparatus.

Conventional COM printers have utilized both CRT and laser imagingoptics with some success. However, there is room for improvement. Forexample, CRT printers for COM use, such as disclosed in U.S. Pat. No.4,624,558 (Johnson) are relatively costly and can be bulky. Laserprinters, such as disclosed in U.S. Pat. No. 4,777,514 (Theer et al.)present size and cost constraints and can be mechanically more complex,since the laser imaging system with its spinning polygon andbeam-shaping optics must be designed specifically for the printerapplication. In addition, laser printers exhibit high-intensityreciprocity failure when used with conventional photosensitive media,thus necessitating the design of special media for COM use.

More recent technologies employed for COM imaging include use of lineararrays such as linear light-emitting diode (LED) arrays, for example, asare used in the Model 4800 Document Archive Writer, manufactured byEastman Kodak Company, Rochester, N.Y. Another alternative is use of alinear light-valve array, such as is disclosed in U.S. Pat. No.5,030,970 (Rau et al.) However, with exposure printheads using lineararrays, COM writers continue to be relatively expensive, largely due tothe cost of support components and to the complexity of driveelectronics. There is a long-felt need to lower cost and reduce size andcomplexity for COM devices, without sacrificing performance orrobustness.

A well-known shortcoming of conventional COM printers relates to the useof microfilm for standard document page sizes. Conventionally, microfilmhas been used for 11×14 inch computer output documents, for letter-sizeddocuments (8.5×11 inches) or for A4 size documents (approximately8.27×11.69 inches, 210×297 mm). Standard 16 mm microfilm allowsdocuments having these sizes to be reduced by suitable factors,typically ranging from 20× to 50× reduction. Using different reductionratios, documents can be arranged in different ways along the film. Forconventional 16 mm film, there are standard simplex or “1-up”arrangements at lower reduction ratios and “2-up” arrangements at higherreduction ratios, with ratios often commonly agreed upon by COMequipment and media manufacturers. However, the use of 16 mm microfilmseverely constrains the maximum size of documents that can be faithfullypreserved in reduced form. For storage of larger documents, such as A2size (16.54×23.39 in, 420×594 mm) or larger, 16 mm microfilm isunsatisfactory.

To store larger documents, a larger format microfilm, such as 35 mmmicrofilm, may be more appropriate. The larger 35 mm format allowshigh-quality digital printing of A2 and larger documents onto COM mediaat standard reduction ratios. For example, engineering drawings thathave traditionally been archived using aperture cards may now beconveniently stored on 35 mm microfilm using digital COM film writers.

Relatively new for digital printing applications, the 35 mm film allowsgreater potential flexibility not only for storage of larger documents,but also where documents may need to be stored at lower reductionratios. Some types of documents, for example, may have image contentsuch as fine lines or highly detailed areas that cannot be faithfullypreserved at 24:1 or greater reduction. Both for larger documents athigh reduction ratios and for smaller documents, the 35 mm media alsoallows enhanced flexibility, allowing alternate arrangements of imageson the COM media. For example, different arrangements could be proposedfor storing color separations, such as red, green, and blue additivecolor separations or cyan, magenta, and yellow subtractive colorseparations, where the separations themselves are printed on COM mediain monochromatic or grayscale form.

Some types of COM printing apparatus have been designed to print ontothe larger 35 mm microfilm media and thereby provide the advantages thatresult from enhanced flexibility of image formats. As one example, theMicrobox Polycom Laser Plotter manufactured by Microbox, located in BadNauheim, Germany is a COM imaging apparatus employing laser scanning,designed to use 35 mm format. However, conventional COM printingapparatus that are designed for imaging onto the larger-format 35 mmmedia do not provide efficient and affordable solutions for imaging ontothe smaller-format 16 mm media. Using conventional COM imaging optics,the cost and complexity of a COM printing apparatus can be prohibitive.For example, when compared against optical requirements for 16 mmimaging, use of the larger 35 mm format requires proportionally largerbeam incident angles in an apparatus using scanning techniques such aslaser and CRT devices employ. Complex and expensive optical componentsare needed in order to suppress the effects of increased aberration. Inrotating polygon systems, for example, motion-induced optical artifactsare substantially more pronounced when imaging in a larger 35 mm format.In the case of linear array printing methods, extending printhead lengthto suit the larger 35 mm format also requires considerably more cost andcomplexity than are needed for 16 mm imaging.

In addition to cost and complexity disadvantages of conventional 35 mmCOM imaging apparatus, conventional COM imaging approaches make theseapparatus inherently less efficient for smaller-format 16 mm imaging.There are no throughput benefits in imaging to a smaller-format COMmedia, since conventional scanning designs fix scan sequences, sweepangles, and timing to suit larger-format media. Likewise for lineararray imaging devices, imaging onto a smaller-format media is lessefficient, since only a portion of the available printhead optics can beused. The above-mentioned drawbacks of increased cost and complexity andreduced efficiency render conventional approaches unsatisfactory forvariable-format COM imaging in a cost-sensitive and efficiency-drivenmarket.

A further drawback of conventional COM imaging approaches relates toproductivity constraints inherent to scanning and to line array imagingdevices. Conventional COM imaging methods, which operate generally byexposing pixels in a line-by-line fashion, are not easily adapted totake advantage of expanded possibilities for using varied imagingformats and of opportunities for writing multiple images in a singleexposure.

An attempt at designing an apparatus capable of addressing these needswas presented in U.S. Pat. No. 6,552,740 (Wong et al.) which depicts amonochromatic printer based on spatial light modulator technology. Priorart U.S. Pat. No. 6,580,490 (Wong et al.) also demonstrates the use of aliquid crystal on Silicon (LCOS) device for printing in multipleformats. U.S. Pat. No. 6,480,259 (Wong et al.) depicts a printer capableof selecting light sources. However, LCOS devices and the surroundingoptical system are thermally sensitive. While the prior art printer cancreate images at an image plane, variations in temperature at the LCOSdevice can alter the image uniformity and quality. Knowledge of thiseffect can be utilized to improve the design by not only controlling thetemperature gradients to prevent unwanted uniformity changes, but tocorrect uniformity errors already present in the printing system.

Thus, it can be seen that there is a need for an improved COM printingapparatus that is inexpensive, compact, and robust, and that allowsprinting in any of a plurality of output media formats, includingprinting of multiple images at one time while maintaining thermalcontrol of the system.

An additional application within the field of printing is that ofprinting of x-ray images. X-ray images are printed on dry silver mediaas well as wet processed silver. These black and white images arecreated through infra-red exposure. Available printers for imaging thedigital data on dry silver media include laser based printers. With theincrease in digital capture, the need for low cost, high speed enginesfor writing on dry silver will increase. Use of spatial light modulatorsin such printing applications will help reduce cost. In additions, drysilver media is thermally processed. Consequently, care must be taken toprovide a thermally controlled environment at the media.

Thus, it can be seen that there is a need for an improved printingapparatus that is inexpensive, compact, and robust, and that isthermally controlled for optimal use.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a printing apparatususing a spatial light modulator for imaging onto a photosensitivemedium, where thermal control is maintained for improved image quality.

With the above object in mind, the present invention provides a printingapparatus for recording an image from digital image data onto aphotosensitive medium disposed at an image plane, wherein thephotosensitive medium presents, at the image plane, a width dimensionthat is selected from of a plurality of width dimensions, the printingapparatus comprising:

-   -   (a) a media supply adapted to supply, at the image plane, the        photosensitive medium;    -   (b) a control logic processor capable of controlling the        operation based on the digital image data;    -   (c) an image forming assembly for directing, onto the        photosensitive medium disposed at the image plane, an exposure        beam for printing, the image forming assembly comprising:        -   (1) a light source for providing light exposure energy for            imaging onto the light sensitive medium;        -   (2) a first lens assembly for directing the light exposure            energy to a spatial light modulator;        -   (3) a beamsplitter which directs the light exposure energy            to the spatial light modulator;        -   (4) the spatial light modulator having a plurality of            individual elements capable of modulating the state of the            light exposure energy to provide an exposure beam for            printing, a state of each of the elements controlled by the            control logic processor according to the digital image data;        -   (5) a temperature profile control apparatus for controlling            a temperature profile of the spatial light modulator; and        -   (6) a second lens assembly for directing the exposure beam            onto the light sensitive medium.

According to an aspect of the present invention, exposure light ispassed through a uniformizer or integrator to provide a source ofspatially uniform, light for the printing apparatus. The light is thenpolarized and passed through a beamsplitter, which directs a polarizedbeam onto a spatial light modulator. Individual array elements of thespatial light modulator, controlled according to digital image data, areturned on or off in order to modulate the polarization rotation of theincident light. Modulation for each pixel can be effected by controllingthe level of the light from the light source, by control of the drivevoltage to each individual pixel in the spatial light modulator, or bycontrolling the duration of on-time for each individual array element.The resulting light is then directed through a lens assembly to exposethe photosensitive medium.

An advantage of the present invention is that it allows a singlemonochrome printing apparatus to be used with microfilm having one of aset of allowed widths. A COM equipment operator using a printer of thepresent invention has the option to load photosensitive media havingdimensions that best suit the type of documents being stored.

A further advantage of the present invention is that it providespotential productivity gains by allowing a COM printer to print byexposing multiple separate images onto photosensitive medium at onetime. This can allow writing multiple images simultaneously to the sameCOM film or to two separate films loaded in the COM printer.

A further advantage of the present invention is that it provides theflexibility for imaging in multiple output formats without increasingthe complexity or cost of the optical system.

A further advantage of the present invention is that it allows largerformat COM imaging without compromising throughput speed.

A further advantage of the present invention is improved image qualitythrough thermal control of the temperature profile at the spatial lightmodulator.

A further advantage of the device is improved image quality throughthermal control of the optical elements.

A further advantage of the system is use in thermally processed printingapplications through temperature control at the media plane.

These and other objects, features, and advantages of the presentinvention will become apparent to those skilled in the art upon areading of the following detailed description when taken in conjunctionwith the drawings wherein there are shown and described illustrativeembodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing outand distinctly claiming the subject matter of the present invention, itis believed that the invention will be better understood from thefollowing description when taken in conjunction with the accompanyingdrawings, wherein:

FIG. 1 is a schematic view showing a printing apparatus of the presentinvention;

FIG. 2 is a schematic view showing image forming assembly components fora printing apparatus of the present invention;

FIG. 3 is a plan view that illustrates a front surface of a multiplesite spatial light modulator;

FIG. 4 shows a cross-section of a reflective modulator with motioncontrollers, a liquid crystal spatial light modulator, a cover glass,and a polarization compensation component;

FIGS. 5 a–5 d illustrate the effect of dithering an un-apertured spatiallight modulator using four distinct image positions;

FIG. 6 is a plan view that illustrates a front surface of asub-apertured spatial light modulator;

FIG. 7 is a cross-sectional view of a reflective spatial lightmodulator;

FIGS. 8 a–8 d illustrate the effect of dithering an apertured spatiallight modulator using four distinct image positions;

FIG. 9 is a schematic view showing image forming assembly components fora printing apparatus of the present invention, including an intermediateimage plane for inclusion of a dither mask;

FIG. 10 is a schematic view showing image forming assembly componentsfor a printing apparatus of the present invention, using an alternativearrangement of image forming assembly components;

FIG. 11 is a schematic view showing image forming assembly componentsfor a printing apparatus of the present invention, showing analternative arrangement utilizing a transmissive LCD;

FIG. 12 is a plan view showing a two-dimensional arrangement of LEDsused as part of a light source selector;

FIG. 13 is a cross-sectional view of an apparatus for holding LEDs andcollimating lenses for LEDs;

FIG. 14 is a plan view of a rotatable wheel of LEDs used as part of alight source selector;

FIG. 15 a is a schematic view of exposure optics showing an arrangementusing multiple reflective spatial light modulators;

FIGS. 15 b and 15 c show possible horizontal and vertical arrangement ofspatial light modulators relative to a beamsplitter component;

FIGS. 16 a and 16 b are schematic views of exposure optics showingalternate arrangements using multiple reflective spatial lightmodulators;

FIGS. 17 a and 17 b are plan views that illustrate prior art layoutformats using a narrow-width COM media;

FIGS. 18 a–18 d are plan views that show additional possible layoutformats using a larger-width COM media;

FIGS. 19 a and 19 b are plan views that show possible layout formatsthat are imaged in a single exposure onto multiple segments of COMmedia;

FIGS. 20 a and 20 b are plan views that show possible layout formatsthat are imaged in a single exposure onto a narrow-width COM media;

FIGS. 21 a–21 d are plan views that show possible layout formats imagedin a single exposure onto a larger-width COM media;

FIGS. 22 a and 22 b are plan views that show additional possible layoutformats that are imaged in a single exposure onto multiple segments ofCOM media;

FIG. 23 a is a side view of a spatial light modulator with TEC;

FIG. 23 b is a side view of a spatial light modulator with heater;

FIG. 23 c is a side view of a spatial light modulator with heat sink;

FIG. 23 d is a side view of a spatial light modulator with a fan;

FIG. 24 is a perspective view of a spatial light modulator with amulti-element temperature profile controller;

FIG. 25 is a perspective view of a beamsplitter with a temperaturecontrolled housing; and

FIG. 26 is a perspective view of a temperature controlled platen.

DETAILED DESCRIPTION OF THE INVENTION

The present description is directed in particular to elements formingpart of, or cooperating more directly with, apparatus in accordance withthe invention. It is to be understood that elements not specificallyshown or described may take various forms well known to those skilled inthe art.

It must be noted that the following description focuses primarily on COMapplications. However, the method and design disclosed herein can beemployed with other types of digital printers, including polychromaticapplications as well as infrared printers. In general, the designdisclosed herein is well suited for printing two dimensional swaths.

Referring now to the drawings, wherein like reference numerals representidentical or corresponding parts throughout the several views, FIG. 1illustrates an archival printer according to the present invention, suchas a COM printer, referred to in general by numeral 100. Printer 100comprises an image forming assembly 10 and a media handling subsystem212. Media handling subsystem 212 comprises a media supply 202, which istypically a film supply, an exposure section 204, an optional filmprocessor 206, and a film storage unit 208. A control logic processor210, such as a microprocessor or other computer adapted to controlprinter 100, accepts and processes image data for printer 100 andcontrols the overall operation of image forming assembly 10 and mediahandling subsystem 212 components. The operation of printer 100 isstraightforward, following the general pattern used for COM printersoverall. To print, an undeveloped section of a photosensitive media 160is advanced from media supply 202 into exposure section 204. Imageforming assembly 10 cooperates with control logic processor 210 to printimage data onto photosensitive media 160. The exposed section ofphotosensitive media 160 is then ready for processing in order todevelop the image. In one embodiment, in which printer 100 usesdry-processed media, film processor 206 may be built into printer 100itself, as is represented in FIG. 1. The exposed section ofphotosensitive media 160 is advanced to film processor 206, where thelatent exposed image is developed using a heat process. For printer 100designed for aqueous (AgX) media, the image development function ofprocessor 206 is carried out by a separate developing apparatus (notshown), using conventional silver-halide film development chemicals andtechniques. For printer 100 using aqueous media, film storage unit 208is typically a cassette, designed to keep the exposed photosensitivemedia 160 protected from ambient light and to provide a means fortransfer of media 160 to the separate developing apparatus.

It is instructive to note that media supply 202 can provide COM mediahaving a number of different sizes and formats. For example, mediasupply 202 could comprise a single roll 252 of photosensitive media 160for imaging. Photosensitive media 160 could be, for example, 16 mm or 35mm film. Alternately, media supply 202 could comprise multiple rolls 252of photosensitive media 160, placed side by side. For example, mediasupply 202 could provide two rolls 252 of 16 mm film in juxtapositionfor imaging, where two or more images are simultaneously exposed, as isdescribed subsequently. Regardless of media dimensions or number ofrolls 252, the general image processing sequence described herein wouldapply.

Referring to FIG. 2, there is shown image forming assembly 10 whichcomprises illumination optics 11 and a first lens assembly 41.Illumination optics 11 comprises a light source 29 which is selectableand can be implemented using a number of types of lamp orelectro-optical components, as is described subsequently. If lightsource 29 comprises a halogen lamp, it is advisable to incorporate afilter 31 or sequential filter such as a filter wheel 32 following thelamp assembly for selecting the appropriate wavelength band. Forexample, for a COM application an infrared rejecting filter may benecessary. For an application employing dry silver media, the filter maypass only the infrared following the lamp in the assembly, as shown inFIG. 2. Light emitted from light source 29 is focused by a lens 37 anddirected to a uniformizer 35.

Uniformizer 35 comprises two field lenses 36 and 42 and a lenslet arrayassembly 40, acting as an uniformizer for the light. Lenslet arrayassembly 40 includes two lenslet arrays 40 a and 40 b. Lenses 36 and 37direct the light into the entrance aperture of lenslet array assembly40. Conjugate planes within image forming assembly 10 are indicated bydotted lines 28.

The light at the intermediate illumination plane is broken into a numberof portions equivalent to the number of elements in lenslet array 40 a.The individual portions are then imaged and magnified by second lensletarray 40 b and second field lens 42. Light passing through uniformizer35 is directed within first lens assembly 41 to a field lens 44, ispassed through an optional aperture stop 46 and a relay lens 48. Relaylens 48 is positioned immediately before a polarization beamsplitterelement 50. It should also be noted that, although relay lens 48 andfield lens 44 are shown as separate elements in FIG. 2, a singlecompound lens (not shown) providing uniform illumination could beemployed instead of the two individual lens elements 48 and 44 as isdepicted in FIG. 2.

Because polarization beamsplitter element 50 may not provide adequateextinction between s-polarization state of light 142 (not shown) andp-polarization state of light 144 (not shown), an optional linearpolarizer 38 may be incorporated prior to beamsplitter element 50. Thereare several places where a linear polarizer 38 can be placed; one suchposition is immediately preceding lenslet array assembly 40. Linearpolarizer 38 is used to isolate the polarization state parallel to theaxis of polarization beamsplitter element 50. This serves to reinforcethe polarization state determined by polarization beamsplitter element50, decrease leakage light and thereby increase the resulting contrastratio. Referring again to FIG. 2, light of the s-polarization state 142passing through polarization beamsplitter element 50 is directed to theplane of a reflective spatial light modulator 52, which is a reflectiveLCD in the preferred embodiment. The p-polarization state 144 is passedthrough beamsplitter element 50. A first lens assembly 41 for directingthe polarized light to the spatial light modulator 52 comprises fieldlens 44, relay lens 48, and polarization beamsplitter element 50.

Referring to FIG. 3, spatial light modulator 52 of this system isdesigned for a two dimensional reflective polarization-based spatiallight modulator. Spatial light modulator 52 includes a plurality ofmodulator sites 53, each of which can be individually modulated. Lightpasses through spatial light modulator 52, is reflected off the backreflective surface of spatial light modulator 52, and returns throughspatial light modulator 52 to be directed through a second lens assembly132, which acts as a print lens assembly, onto an image plane 150 (FIG.2). If a modulator site 53 is “on” or bright, during the round-tripthrough spatial light modulator 52, the polarization state of the lightis rotated. In an ideal case the light is rotated 90 degrees when site53 is in an “on” state. However, this ideal degree of rotation is rarelyeasily achieved. If a given modulator site is “off” or dark, the lightis not rotated. The light that is not rotated is not passed straightthrough beamsplitter element 50 but is redirected away from the mediaplane by polarization beamsplitter element 50. It should be noted thatlight which is rotated by spatial light modulator 52 may becomeelliptically polarized. Upon passing through a linear polarizer, thelight will regain linearity. However, light that is not passed through alinear polarizer will retain ellipticity.

As noted above, the most readily available choice from among reflectivepolarization based modulators is the reflective liquid crystalmodulator. Such modulators, originally developed for use in projectiondisplay, can have thousands of modulator sites along each orthogonaldimension, with footprints as small as a 0.9 inch diagonal. These highresolution reflective LCDs are often twisted nematic LCDs orhomeotropically aligned reflective LCDs, although other types ofreflective LCDs such as ferroelectric are often employed in projectiondisplay. Some of the key characteristics of these LCDs are highresolution, high contrast (>100:1), fast frame rate of 70 frames persecond or higher, and high aperture ratios (>90%). In addition, theincorporation of a CMOS backplane increases the uniformity across thearray. The LCDs are also capable of producing an eight bit or greatergray scale either through pulse width modulation or through analogoperation. In either case data is introduced digitally to the printingsystem, as controlled by control logic processor 210 (FIG. 1). Thesecharacteristics ensure that the reflective LCD is an excellent choicefor use in a reflective printing system.

Spatial light modulator 52 can be designed in a number of differentconfigurations. The most amenable to a low cost printing system is asingle chip system. In the preferred embodiment, spatial light modulator52 would be a single-chip device having a large number of pixels,specifically designed for single color use, providing optimum framespeed.

Because of cost and availability constraints, it may be necessary to usea specific design of spatial light modulator 52 that is not optimizedfor the wavelength used. In such a case, there are methods for obtainingoptimum performance. For example, for a given liquid crystalcomposition, thickness, and applied voltage, the resulting polarizationrotation on an incident beam may vary with wavelength so that theefficiency and contrast of the modulation can vary as a function ofwavelength. In the bright, or “on” state, this difference in rotationcan effect the efficiency of the system. In other words, the percentageof incident light that is actually rotated and imaged on the media planecan vary. This difference in wavelength efficiency can be accounted forby adapting the illumination strength and exposure time, based onwavelength, in order to obtain the power density required by the media,using techniques well-known in the imaging art. The problem isparticularly acute in the dark or “off state.” In this state, the lightis not rotated and should not be directed though polarizationbeamsplitter element 50 and imaged. If the light is in fact, rotated,light will leak through the imaging system and decrease the contrast.

In an alternate embodiment, contrast can be adjusted for wavelengthusing polarization compensation or selection devices. Referring to FIG.4, in which a cross-sectional view of spatial light modulator 52 isshown, a polarization compensator 76 may be introduced to the surface ofspatial light modulator 52. As shown in FIG. 4, the top surface or layerincludes compensator 76, the second surface or layer is a cover glass 74of spatial light modulator 52, the third layer is spatial lightmodulator 52 itself, with a reflective backplane. Behind spatial lightmodulator 52 are mounted actuators 70, 72 or mounts for actuators toposition spatial light modulator 52.

An alternate method for contrast adjustment is to incorporate apolarization compensator in the path of the optical beam to correct thepolarization state of the light. A single compensator may be placed inthe optical path to particularly correct the off-state of the light.However, polarization compensation devices can be expensive. Anefficient but inexpensive means to accomplish the same results can beobtained using linear polarizers. As was mentioned earlier, a single LCDimparts a degree of polarization rotation dependent on the color ofillumination. In an effort to maximize contrast, special care must betaken to provide a truly dark “off state”. Because the rotation of thelight from spatial light modulator 52 is not always crossed perfectlywith beamsplitter element 50 in the off state, additional polarizationselection must be incorporated into the optical path. Also, polarizationbeamsplitter element 50 is not perfect and will leak some amount oflight. For these reasons, an additional sheet polarizer can be disposedeither immediately before or after second lens assembly 132. Thisadditional polarizer serves to reject leakage light that is passedthrough polarization beamsplitter element 50. Specifically, for aparticular LCD modulator, the dark state of the light is actuallyrotated 7 degrees from the polarization transmitting direction ofpolarization beamsplitter element 50. To correct this in the preferredembodiment, a second polarizer 134 (FIG. 2) is provided, rotated 7degrees off-axis to suppress leakage light. The particular angle atwhich polarizer 134 must be placed is a function of the particularreflective LCD chosen for the printing system. A suggested placement ofpolarizer 134 in the optics path is shown in FIG. 2.

Contrast modification is an application dependent adjustment. For thecase of photographic printing, the required contrast may be quite low.The contrast need not be optimized. In some case it may even be reducedthrough the same mechanisms as contrast enhancement. For example, awaveplate or polarizer rotated off the optimal axis will reducecontrast.

Furthermore, in the case of polychromatic printing, the contrastrequirement of the media varies as a function of wavelength. So, thesystem would be employed in a color sequential manner. Each colorcomponent would illuminate the device independently, and the contrastwould be adjusted accordingly. Contrast adjustment can either beaccomplished optically, or through the address of the modulator. Theaddress voltage to the modulator can vary sequentially as a function ofillumination wavelength.

Dithering

In an alternative embodiment of printer 100, dithering may be used toincrease the inherent LCD resolution and to compensate for modulatorsite defects. A dithering pattern for a standard high aperture ratio LCDmodulator 52 is shown in FIGS. 5 a–5 d.

To dither a full aperture LCD is to image the spatial light modulator 52at one position, and reposition spatial light modulator 52 a fraction ofa modulator site distance away and image. In so doing, multiple imagesare created and overlapped. By overlapping multiple images, the systemacquires a redundancy that corrects for modulator site failure or dropout. Furthermore, by interpolating or updating with new data betweenpositions, the effective resolution is increased. Referring to theexample dithering scheme depicted in FIGS. 5 a–5 d, spatial lightmodulator 52 is first positioned at a first modulator position 61 andmodulator sites 63 are positioned and imaged (FIG. 5 a). Spatial lightmodulator 52 is then moved to a second modulator position 62 (FIG. 5 b)which is one half of a modulator site laterally displaced from previousposition 61. Spatial light modulator 52 is then imaged at position 62.Spatial light modulator 52 is then displaced one half of a modulatorsite longitudinally from previous position 62, which means it isdiagonally displaced from initial position 61 to a third modulatorposition 64 (FIG. 5 d). Modulator sites 63 are illuminated and the mediaexposed again. Spatial light modulator 52 is then moved to a fourthmodulator position 65 that is laterally displaced from third position 64(FIG. 5 c). The media is then exposed at this position. Using thispattern, there is effectively a fourfold increase in the amount of datawritten. This serves to increase image resolution and provide means tofurther sharpen images. Alternately, with a high aperture ratio, it maybe sufficient to simply dither in one diagonal direction (that is, forexample, from first position 61 shown in FIG. 5 a to third position 64shown in FIG. 5 d) in order to achieve suitable results.

Dithering requires motion of the modulator in at least one direction.Each increment of motion is approximately between 5 um and 20 um for atypical reflective LCD modulator. In order to achieve this incrementalmotion, many different actuator 54 or motion assemblies, as shown inFIG. 2, can be employed. For example, the assembly can use twopiezo-electric actuators.

In an alternate embodiment for dithering, requiring minimum modificationto a reflective LCD device designed for projection display, the devicecan be sub-apertured. In an effort to markedly increase resolution, themodulator can contain an aperture ratio that is relatively small.Ideally this aperture must be symmetrically placed within each modulatorsite. The result is a modulator site for which only a fraction of thearea transmits light. Referring to FIG. 6, there is shown anillustration of a sub-apertured area modulator. Black regions 80represent the non reflecting, non-transmitting regions of the device.Clear areas 82 represent the sub-apertured transmitting areas of theLCD.

FIG. 7 is a cross-sectional view of an alternate two-dimensional LCDspatial light modulator 52′. There is a frame 78′ which can be in theform of a CMOS backplane on top of which rests an LCD 76′. Above the LCD76′ is a cover glass 74′. Sub-apertures, to effect the pattern of FIG.6, may exist as a mask in frame 78′, as a pattern in LCD 76′, or as apattern on the surface of cover glass 74′ closest to LCD 76′. In aneffort to double the resolution in each direction, a sub-aperture ofapproximately 25% may be employed. By dithering a 25% aperture ratiodevice, it is possible to double the resolution in the image.

FIGS. 8 a–8 d represent the dithering of a sub-apertured device. Spatiallight modulator 52 is positioned at a first modulator position 84 (FIG.8 a) and sub-apertured modulator sites 92 are positioned and exposedwhile darkened (non reflecting) regions 94 are not imaged ontophotosensitive media 160. Spatial light modulator 52 is moved to asecond modulator position 86 (FIG. 8 b) a half full modulator site(sub-aperture and surrounding non-reflective area) laterally displacedfrom previous position 84. Spatial light modulator 52 is then exposed atposition 86. Spatial light modulator 52 is then displaced a half a fullmodulator site longitudinally from previous position 86 to thirdmodulator position 88 (FIG. 8 c), which means it is diagonally displacedfrom the starting point at first modulator position 84. Spatial lightmodulator 52 is then illuminated and the media exposed again. Spatiallight modulator 52 is then moved to a fourth modulator position 90 (FIG.8 d) that is laterally displaced from third position 88. The media isexposed at this position. Effectively, there is a four times increase inthe amount of data written. This serves to increase image resolution andto provide means for further image sharpening. A sub-aperture of 25% byarea, as approximated in FIG. 6, will give the highest image quality fora four step dither, however, in an effort to allow for redundancy in themodulator sites, it is better to use a sub-aperture ratio of greaterthan 25% by area.

When the sub-apertures are not placed symmetrically within each cell,dithering becomes quite difficult. Different periods of motion can beemployed; for instance, one full modulator site width lateral motioncombined with half a modulator site vertical motion makes a ditherpattern. However, such motion is quite prone to image artifacts. Asimple way to get around this problem is to dither using only oddcolumns, then repeat the dither using only even columns. Alternately,the dither algorithm may follow another pattern, dithering even rows,then dithering odd rows, for example.

In an alternate embodiment, spatial light modulator 52 is leftun-dithered. But, dithering takes place in one of conjugate image planes28 as is shown in FIG. 9. In this conjugate plane 28 a mask 184containing the sub-aperture is placed. It is mask 184 that is ditheredwhile the information content to the modulator sites at spatial lightmodulator 52 is updated. This allows a sub-apertured image to berecorded although the device may not be sub-apertured. It is alsopossible to create an intermediate image plane, however, this will provecumbersome.

Another means by which to accomplish the dithering through the use ofmask 184 is to place mask 184 in the image plane immediately beforemedia 160. This mask 184 can then be dithered while data is refreshed tothe device between dither positions. This method of dither willaccomplish the same effect as the previous method of the intermediateimage.

Following spatial light modulator 52 and polarization beamsplitterelement 50 in FIG. 1 is second lens assembly 132. Second lens assembly132 provides the correct demagnification of the image of spatial lightmodulator 52 to image plane 150 where photosensitive media 160 islocated. It should be noted that second lens assembly 132 can beconfigured for reduction (as is needed for micrographics in thepreferred embodiment) or for magnification (as is needed for diagnosticimaging). The configuration of second lens assembly 132 components isdependent on how printer 100 is used. With this arrangement, the sameillumination optics 11 and spatial light modulator 52 components can beused with different printer 100 types.

The optical system designed using the arrangement disclosed in FIG. 1has been shown to be compact, low in cost, and efficient. Thecombination shown in FIG. 1, using a high intensity light source 29 andsupporting illumination optics 11 with a reflective LCD spatial lightmodulator 52 and second lens assembly 132 optics optimized forCOM-quality reduction, provides high levels of exposure energy suited tothe resolution and contrast requirements of the micrographicsenvironment. Moreover, because image forming assembly 10 is capable ofproviding high exposure energy, image forming assembly 10 allows printer100 to use dry-process media when provided with a light source havingsufficient power and wavelength characteristics, thereby providingperformance and environmental benefits.

Achieving Grayscale Output

Printer 100 is capable of achieving sufficient uniformity whileretaining the grayscale performance. Most spatial light modulators 52alone can receive up to 8 bits of bit depth. However, 8 bits to themodulator may not translate to 8 bits at the media. Furthermore, LCDmodulators are known to exhibit some measure of roll-off or loss ofcontrast at the edges of the device. To print an adequate grayscalerange and provide additional bit depth, the present invention can takeadvantage of the fact that spatial light modulators 52 designed forprojection display generally refresh data faster than is required forprinting. Consequently, it is possible to create a single image at themedia 160 as a super-position of a series of images. The individualimages that comprise the final image can vary both in informationcontent and illumination.

It is possible to maintain the same image data at spatial lightmodulator 52 and, by altering the illumination level from light source29, introduce additional bit depth. By varying the illumination level,(and/or duration), and by altering the data content controlling spatiallight modulator 52, printer 100 can build a composite image out of aseries of preliminary images. The superposition of the images of variedinformation content and varied illumination level introduces additionalbit depth to the composite image.

Non-uniformity Compensation

Using the present invention, printer 100 can control image formingassembly 10 to correct for some non-uniformity such as roll-off atspatial light modulator 52 edges. One way to accomplish this is tointroduce additional image data to spatial light modulator 52,activating only individual modulator sites 53 on the outer edge ofspatial light modulator 52. These added images can then be exposed andsuperimposed on the other images thus giving additional depth to theedge regions. An example method would be to scan a series of imagestaken at LCD spatial light modulator 52, create data maps and convolveall input data with an initial map of LCD spatial light modulator 52 tocorrect the image. Similar techniques can be used to adjust formodulator non-uniformities that are known prior to operation.

Thermal Compensation for Non-uniformity and Spatial Light ModulatorOperation

The uniformity of a flat field projected from a spatial light modulatoris directly related to the temperature of operation and thecorresponding temperature profile. In particular, when using a LCOSdevice, there is an optimal operating temperature. The brightness(reflectance) as well as contrast are optimized at a given temperature.This temperature is often higher than room temperature. For example, theoptimal temperature may be 45 C. It becomes necessary then to controlthe operating temperature of the device. As the temperature drifts, sowill the device performance.

This situation is further complicated when the temperature profile atthe device is spatially varying. If there is a spatial gradient to thethermal profile at the device, there will be a correspondingreflectance, brightness, contrast, and resulting uniformity gradient.The immediate solution is to control the temperature of the device 52 orthe surrounding area to be a predetermined constant. This control mayeither be achieved by heating or cooling. One method is to control theenvironmental temperature through localized temperature control such asair circulation or a fan 253 as is shown in FIG. 23 d. Another is toprovide a heat sink 57 at the device, a heater 56, or a thermo-electriccooler (TEC) 55 behind the spatial light modulator (behind or integratedwith the back of the device) to control the temperature as is shown inFIGS. 23 a–d.

Another complication arising from the manufacturing process is thestress at the device. A device manufactured at a fixed temperature maydisplay a certain flatness or curvature at that temperature. Theflatness corresponds to a flat field uniformity. At a differenttemperature the uniformity of the light reflected off (or transmittedthrough) the imager maybe completely different. Controlling thetemperature can allow the device to contain a signature flatness oruniformity that can be corrected out using image data manipulation.

Alternatively, if the response of the device is known both for everyspatial location as well as a function of temperature, the operatingsystem can contain a map. This map or temperature profile would allowcalculation of a 2-dimensional thermal profile, that when maintained atthe device, delivers the best system uniformity. In effect, the spatialthermal gradient can provide a calculated profile that corrects forimage non-uniformities not only at the device, but elsewhere in thesystem. Such an arrangement would require means to control thetemperature at the device as is shown in FIG. 24 where the reflectivespatial light modulator 52 has a multi-element temperature control 58with individual elements 59 on the back of the device 60 (the back ofthe device may be the reflective side 60 of the device 52).

The second thermally sensitive element is the beamsplitter. Inparticular, if a polarizing beamsplitting cube 50 is employed thetemperature at the cube must be maintained and not provide a stronggradient. The coatings and adhesives in such a cube can cause variationsin transmission and reflection as a function of temperature. Thesevariations can also vary as a function of wavelength. Using airtemperature control surrounding the cube may provide advantages.Alternatively, the cube mount 51 can contain temperature control whilemaintaining clear windows 67 as is shown in FIG. 25.

The third thermally sensitive point is the media plane. In particular,when used with thermally sensitive media, it is important that the mediaplane not impart either a temperature gradient, or simply overheat andactivate the media. Controlling the environmental temperature throughair cooling or heating is one option. The other is to use a temperaturecontroller 152 to heat, cool, or sink the platen 151 at image plane 150as is shown in FIG. 26.

Color Sequential Operation

For applications such as photofinishing, printing is fundamentallypolychromatic. There is different data for each color plane anddifferent operating conditions for the system. First, the light sourcemust be capable of illuminating the modulator color sequentially. Thiscan be accomplished by color sequentially operating LEDs, lasers orother individual light sources. Alternative a lamp with a filter wheelcan be employed. Data must be provided to the spatial light modulatorcolor sequentially. The illumination must correspond with the dataprovided at the spatial light modulator. The operating conditions of themodulator such as the operating voltages, the electro-optics response,and any color specific look up tables should be provided to themodulator in synchronous with the illumination. It is possible that therequired contrast or media sensitivity will vary with color. Theappropriate voltages, uniformity maps, and look up tables need to beprovided with the color specific data and illumination. This may requirealtering the backplane voltage as a function of illumination wavelength.In addition, it may be necessary to turn off the illumination betweenexposures (even within a single composite image) to allow residuals(residual images) to decay.

Thermal maps may vary with color. While it is possible to update the mapas a function of illumination wavelength and date, it may not bepractical as the thermal time constant may be too slow to enableefficient operation. A single thermal map is a better choice. That mapmay simply be a flat, uniform temperature profile.

Alternative Embodiments for Image Forming Assembly 10 Components

The design of printer 100 allows a number of alternate embodimentswithin the scope of the present invention. Referring to FIGS. 10 and 11there are shown possible alternate arrangements of components for imageforming assembly 10. Notable changes to components include thefollowing:

-   -   (1) Use of alternative light sources. Light sources can include        a lamp and filter. Alternatively lasers (solid state, gas,        fiber) provide an excellent light source as do light emitting        diodes. In the case where the printer is operated color        sequentially, the light source may be a combination of        illumination elements or a lamp with a filter wheel assembly.        -   Most available light sources do not provide sufficient            uniformity on their own. If and when light sources of            sufficient uniformity become available, uniformizing optics            may not be necessary.    -   (2) Use of an alternative uniformizing component, such as an        integrating bar 222 in place of lenslet array assembly 40. While        lenslet arrays, in general, may provide better uniformity,        integrating bar 222 can be an appropriate substitute for        monochromatic printing applications, particularly when using        coherent light sources, such as lasers. The integrating bar may        help to minimize coherence effects. Another method of providing        uniform illumination is to incorporate fibers with a fiber        faceplate or fiber fabric. The uniformizer can be incorporated        into the first lens assembly as can any filters, or        prepolarizers.    -   (3) Use of an alternative to polarization beamsplitter 50. A        pellicle 220 can provide sufficient beamsplitting capability for        monochromatic printing and can offer cost-saving advantages over        polarization beamsplitters 50. Pellicles 220 are well suited to        monochromatic applications, such as is disclosed above (but may        cause image artifacts with polychromatic systems).    -   Specifically, pellicles 220 do not extinguish or redirect light        with the efficiency of a beamsplitting cube. In addition, over a        narrow wavelength band, some pellicles 220 can demonstrate        interference effects. For example, if an optical system were to        have competing narrow wavelength bands, such as 630 nm and 460        nm, interference effects in the different wavelength regions        could cause significantly non-uniform illumination at the        modulator. Additionally, pellicles 220 are more useful in        systems where light intensity is not a major concern, since        pellicles are not designed for applications using high levels of        optical power. It should be noted that, because the pellicle is        not, by itself, a polarization-sensitive device, a prepolarizer        or polarized light source is helpful. If used in image forming        assembly 10 of the present invention, the first polarizer would        eliminate 50% of incident unpolarized light; the pellicle would        then eliminate another 50% of the remaining light. Because of        this, spatial light modulator 52 would receive only 25% of the        potential illumination. It is instructive to note that, in image        forming assembly 10 as described above, light intensity demands        are not severe and illumination is monochromatic for any given        exposure, allowing the use of pellicle 220 as an alternative.        -   Another polarizing beamsplitter consists of a wire grid            polarizer. Such a polarizer can be used in either reflection            or transmission. When using a wire grid polarizer, care must            be taken to choose the appropriate polarization state from            the illuminator.    -   (3) Use of alternate beam-steering components. Suitable        alternatives for beam steering other than use of polarization        beamsplitter 50 or pellicle 220 include a simple turning mirror        or prism.    -   (4) Use of transmissive LCD components for spatial light        modulator 52. For some COM applications, there may be sufficient        resolution and contrast available using a transmissive LCD        spatial light modulator. As is shown in FIG. 11, use of a        transmissive modulator for spatial light modulator 52 removes        the turn in the optics path and can simplify the design.    -   (5) The imaging or printing lens assembly images the light onto        an image plane. The lens assembly can include an exit polarizer        if it is necessary. Furthermore the lens assembly and the        beamsplitter may be one integrated assembly. In order to print a        variety of sizes, the lens assembly may contain lenses on a        turret designed to provide different magnifications, (which may        occur at different image positions). Alternatively, the lens        assembly may contain a zoom lens, or a “quasi-zoom” capable of        imaging at discrete, different magnifications.    -   (6) The media can be selected from a variety of media such as        COM media, AgX media, and dry silver media according to the        application.    -   (7) The media plane or platter 151 may need to be thermally        controlled. Control can be established by controlling the        environment around the media plane or controlling the        temperature at the media plane with a temperature controller        152. For example, the entire media plane can attach to a heat        sink or a heater.

Because of the digital addressability of the LCD device and theflexibility in varying level of illumination, the printing solutionsdescribed above provide an adequate bit depth and reasonable timing foruse in a COM printer. Using the printer of the present invention takesadvantage of economical, commodity LCD technology to produce low cost,high resolution prints, with high productivity.

The use of reflective liquid crystal technology allows for very highresolution two-dimensional printing. Furthermore, the use of dithering,particularly sub-apertured dithering, provides means to further increasethe resolution and avoid artifacts due to modulator site failure.

Preferred Embodiment for Light Source 29

Light source 29 of illumination optics 11 must provide light at awavelength that is best suited to the sensitivity of photosensitivemedia 160. In the present invention, light source 29 is selectable,allowing printer 100 to utilize any of a number of different types ofphotosensitive media 160. In the preferred embodiment, light source 29comprises one or more LEDs, grouped by emitted wavelength. Referring toFIG. 12, there is shown an arrangement of LEDs within a circularaperture 20, for example: red wavelength LEDs 14, green wavelength LEDs16, and blue wavelength LEDs 18. With this arrangement, the LEDs aredistributed so as to provide exposure light evenly. LEDs of a desiredcolor are energized under the control of control logic processor 210,based on the wavelength required for a specific photosensitive media160. Using this illumination method, printer 100 can be automaticallyadapted to use one or another type of photosensitive media 160 and toprovide the required exposure characteristics needed by that type ofmedia 160. For a media 160 that is intended for exposure by red lightonly, control logic processor 210 would enable red wavelength LEDs 14,for example. The illuminator can also be used color sequentially.

Referring to FIG. 13, there is shown a cross-sectional view of red LEDs14, green LEDs 16, and blue LEDs 18 mounted with collimating lenses 32into a frame 19. Individual collimating lenses 32 are optional but mightbe useful to aid in encapsulation and position of LEDs 14, 16, and 18.

Referring to FIG. 14, there is shown another alternative embodimentusing LEDs 14, 16, and 18. A rotatable LED wheel 26 comprises groupedLEDs 14, 16, and 18 that can be rotated into position by control logicprocessor 210 for providing exposure energy. The arrangement of FIG. 14might be most suitable where it is advantageous to obtain concentratedlight energy from a close grouping of multiple LEDs 14, 16, and 18.However, the disadvantage presented using the arrangement of FIG. 14relates to rotation of rotatable wheel 26, since this requires an addedmotor or manual operation. The preferred embodiment would usedistributed LEDs 14, 16, and 18 as shown in FIG. 12, arranged forselective energization as electronically switched by control logicprocessor 210. The arrangement of FIG. 12 requires no moving parts andcan be implemented at lower cost than that shown in FIG. 14.

LEDs 14, 16, and 18 would be specified based on exposure sensitivitycharacteristics of each type of photosensitive media 160 to be used inprinter 100. A number of alternate arrangements are possible, includinguse of LEDs of any suitable color, emitting the desired wavelength. Forexample, different groupings of red LEDs could be used for types ofmedia 160 that differ only slightly in terms of wavelength response. Asingle LED could be used for any one media 160 type; however, the use ofmultiple LEDs provides additional output intensity to be directed byimage forming assembly 10.

Alternate Light Source 29 Options

There are a number of other alternatives for light source 29 that wouldallow the use of multiple types of photosensitive media 160 to be usedby the same printer 100. For example, a halogen lamp could be used toprovide a broadband light beam transmitted through filter elements (forexample, red, green, or blue filter) to provide a monochromatic lightbeams. Optionally, lasers could also be employed as light sources 29.

Automated Sensing of Media 160 Width and Response

As an option, an automated mechanism could be employed to detect thewidth of a loaded photosensitive media 160 and to automatically selectthe appropriate output format based on the width of media 160 detected.Referring back to FIG. 1, a sensor 234, connected to control logicprocessor 210, is disposed to sense an encoding 236 that is coupled tomedia supply 202. There are a number of possible configurations forsensor 234 and encoding 236, including the following, for example:

Where encoding 236 has the form: Sensor 236 would be: Barcode or otheroptical encoding Barcode reader or other opti- cal reader, such asbuilt-in or hand-held scanner. Transponder containing a memory thatTransceiver, such as an RF includes identifying data for the media,transceiver, for example, such as an RF transponder, “SAMPT” “ModelS2000” ™ trans- (Selective Addressable Multi-Page ceiver, available fromTexas Transponder), part number “RI-TRP- Instruments, Incorporated,IR2B” available from Texas Instruments, located in Dallas, Texas,Incorporated. USA. Magnetically encoded strip Magnetic strip readerMemory device, such as an I-button, I-button reader manufactured byDallas Semiconductor Corp., Dallas, TX Trace pattern, such as anembedded trace Trace pattern reader pattern

Encoding 236 could be printed or attached to media 160 packaging orcould be provided from a network connection or manually entered by anoperator. Using this option with the preferred embodiment, upon sensingmedia 160 width from encoding 236, control logic processor 210 wouldrespond by using the preferred output format for imaging onto media 160.Encoding 236 could include dimension data, for example, or could eveninclude instructions or an algorithm that controls printer 100 responseto the media 160 type that is loaded.

A mechanical, electromagnetic, or optical sensor (not shown) couldalternately be used to indicate media 160 width.

It can readily be seen that printer 100 can be adapted to accept media160 in any of a set of widths, with only minor modifications to mediahandling hardware. This would allow, therefore, printer 100 to handle arange of media 160 types, resulting in cost benefits and increasedefficiency.

Output Formats

FIGS. 17 through 22 illustrate some examples of possible layouts foroutput images 250 exposed onto photosensitive media 160 for a COMapplication. It must be stressed that the layouts shown in FIGS. 17through 22 are by way of example, and are not by way of limitation. Manysimilar formats could alternately be used, within the scope of thepresent invention. Images 250 and photosensitive media 160 arerepresentative only and are not drawn to scale.

Referring to FIGS. 17 a and 17 b, there are shown typical layout formatsconventionally used for output images 250 imaged onto photosensitivemedia 160, where media 160 is narrow-width, 16 mm microfilm. Outputimage 250 for FIG. 17 a could be, for example, an A4 sized image at 24×reduction. Output images 250 in FIG. 17 b could be, for example, A4sized images at 40× reduction. The arrangement of FIG. 17 b could beused for the front and back of the same document, for example.

Referring to FIGS. 18 a through 18 d, there are shown exemplary layoutformats for output images 250 imaged onto photosensitive media 160,where media 160 is wider 35 mm microfilm. As FIGS. 18 a through 18 dshow, the use of wider 35 mm microfilm allows reduction of largerdocuments and also allows a flexible number of alternate arrangementsfor other documents. Output image 250 in FIG. 18 a could be, forexample, an A4 sized image at 20× reduction or an A3 sized image at 24×reduction. Output images 250 in FIG. 18 b could be, for example, two A3sized images at 40× reduction or two A4 images at 32× reduction. Outputimages 250 in FIG. 18 c could be, for example, three A4 sized images at32× reduction. The arrangement of FIG. 18 c might be well suited, forexample, for storing grayscale versions of color separations, such asthe additive red, green, and blue separations, or the subtractive cyan,magenta, and yellow separations. Output images 250 in FIG. 18 d couldbe, for example, four A4 sized images. The arrangement of FIG. 18 dmight be well suited, for example, for storing front and back sides oftwo separate documents or for storing four different documents. Usingspatial light modulator 52, output images 250 in FIGS. 18 b, 18 c, and18 d can be exposed simultaneously.

Referring to FIGS. 19 a and 19 b, there are shown exemplary layoutformats for output images 250 imaged onto photosensitive media 160,where media 160 is made up of two widths of 16 mm microfilm, bothdisposed at image plane 150 at the same time. The 2-up arrangement ofFIG. 19 a shows two images in similar format to that illustrated in FIG.17 a. The 4-up arrangement of FIG. 19 b shows four images in similarformat to that illustrated in FIG. 17 b. Using spatial light modulator52, output images 250 in FIGS. 19 a and 19 b can be exposedsimultaneously, effectively doubling the productivity.

Referring to FIGS. 20 a and 20 b, there are shown exemplary layoutformats that can be employed for simultaneous exposure of multipleoutput images 250 onto photosensitive media 160, where media 160 isnarrow-width, 16 mm microfilm. The arrangement of FIGS. 20 a and 20 b issimilar to the arrangement shown in FIGS. 17 a and 17 b, with theadvantage that, using spatial light modulator 52, both output images 250in FIG. 20 a and all four output images 250 in FIG. 20 b can be exposedsimultaneously.

Referring to FIGS. 21 a through 21 d, there are shown exemplary layoutformats for output images 250 imaged onto photosensitive media 160,where media 160 is wider, 35 mm microfilm. Using spatial light modulator52, all output images 250 in each format shown in FIGS. 20 a through 20d can be exposed simultaneously, with substantial gains in throughput.

Referring to FIGS. 22 a and 22 b, there are shown exemplary layoutformats for output images 250 imaged onto photosensitive media 160,where media 160 is narrower, 16 mm microfilm. Using spatial lightmodulator 52, all output images 250 in each format shown in FIGS. 22 aand 22 b can be exposed simultaneously, with substantial gains inthroughput.

As can readily be appreciated from FIGS. 17 through 22, the use ofspatial light modulator 52 provides distinctive advantages for COMoutput imaging, allowing a varied arrangement of output image 250formats onto photosensitive media 160 having a range of widths, evenwhere two rolls of media 252 supply two segments of media 160 asillustrated in FIGS. 19 a, 19 b, 22 a, and 22 b.

Alternative Use of Multiple Spatial Light Modulators

There may be limitations or cost benefits that make it advantageous toemploy multiple spatial light modulators 52 instead of using a single,larger spatial light modulator 52. Referring to FIG. 15 a, there isshown one possible arrangement using multiple spatial light modulators52 a and 52 b, both disposed on the same side of polarizationbeamsplitter element 50. Using such an arrangement, it would be possibleto write different parts of a larger image onto media 160 using tilingtechniques that are familiar in the imaging arts. Alternately, usingmultiple spatial light modulators 52, different documents could bewritten to COM media 160 at the same time, such as to provide the 2-uparrangement shown in the example of FIG. 17 b. Spatial light modulators52 can be disposed in a number of arrangements with respect topolarization beamsplitter element 50. Referring to FIGS. 15 b and 15 c,there are shown possible arrangements of spatial light modulators 52 aand 52 b, disposed horizontally and vertically with relation to eachother. Dotted reference line A in FIG. 15 a corresponds to the samereference line A in FIGS. 15 b and 15 c. Two spatial light modulators 52are shown; however, more than two spatial light modulators 52 could bedisposed horizontally and/or vertically with relation to each other onthe same face of polarization beamsplitter element 50.

Referring to FIG. 16 a, there is shown an alternate arrangement usingmultiple spatial light modulators 52 a and 52 b that are each disposedparallel to a different face of polarization beamsplitter element 50.More than two spatial light modulators 52 could be used, such as toprovide large format or 2-up printing or for the arrangements shown inFIGS. 17 through 22. FIG. 16 b shows yet another possible arrangementusing three spatial light modulators 52 a, 52 b, and 52 c. A number ofother possible arrangements using three or more spatial light modulators52 on different sides of polarization beamsplitter element 50 could beused, in addition to those shown in FIGS. 16 a and 16 b.

The arrangements of FIGS. 15 a, 15 b, 15 c, 16 a, and 16 b could alsoemploy a pellicle 220 for directing the beam as an alternative topolarization beamsplitter element 50.

Using image forming assembly 10 of the present invention, it can be seenthat a single printer 100 can be configured to allow loading ofphotosensitive media 160 having any one of a number of suitable widthdimensions, and to adjust its output imaging characteristics in order torecord output images in an appropriate format for media 160 having thatwidth dimension. Printer 100 can prompt an operator to specify one of aset of available output formats, based on the width dimension detected.

Simultaneous Exposure of Multiple Output Images

As illustrated in FIGS. 17 through 22, use of spatial light modulator 52enables printer 100 to expose multiple images at one time. Thiscapability increases the potential throughput productivity of printer100 and even allows printer 100 to image simultaneously onto twoseparate rolls 252 of media 160 at one time.

To effect simultaneous printing of multiple images, it is only necessaryto provide the spatial light modulator 52 with a composite image made upof the multiple images, so that different selected groupings ofindividual modulator sites 53 are driven to display different images atone time. Referring again to FIG. 3, dotted line L shows a possibledivision of spatial light modulator 52 into two segments or partitions,right and left, for use in 2-up printing. Drive signals for themodulator sites of the two segments originate from a composite imagethat is formed by two different, smaller images placed side by side.Each segment would then be able to write a separate image 250. As justone example, the right half of modulator 52 could expose the rightmostimage 250 of FIG. 20 a at the same time that the left half of modulator52 would expose the leftmost image 250 of FIG. 20 a. Alternately, wheremultiple modulators are used, each modulator is provided with drivesignals from a different image data file at the same time. For example,referring to FIG. 15 a, 16 a, or 16 b, modulator 52 a could be used towrite one image, modulator 52 b to write another image. Numerousalternative ways of driving partitions of a larger modulator and/ormultiple modulators are also possible to effect simultaneous exposure ofmultiple images, with results such as shown in FIGS. 17–22. It can bereadily appreciated that the resulting productivity gains could besubstantial.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the scope of theinvention as described above, and as noted in the appended claims, by aperson of ordinary skill in the art without departing from the scope ofthe invention. For example, photosensitive media 160 could be providedfrom roll 252 or in some other form. Numerous formats are available forthe placement of images onto narrow 16 mm or wider 35 mm media 160. Anumber of modifications could be made to image forming assembly 10components without departing from the scope of this invention.

Therefore, what is provided is a film recording apparatus that providesa plurality of output formats using the same exposure optics, allowingthe recording of images onto different sizes of media in differentformats and allowing the exposure of multiple images at one time.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the scope of theinvention.

PARTS LIST

-   10. Image forming assembly-   11. Illumination optics-   14. Red LED-   16. Green LED-   18. Blue LED-   19. Frame-   20. Circular aperture-   26. LED wheel-   28. Conjugate planes-   29. Light source-   31. Filter-   32. Filter Wheel-   33. Filter-   35. Uniformizer-   36. Field lens-   37. Lens-   38. Linear polarizer-   40. Lenslet array assembly-   40 a. Lenslet array-   40 b. Lenslet array-   41. First lens assembly-   42. Field lens-   44. Field lens-   46. Aperture stop-   48. Relay lens-   50. Polarization beamsplitter element-   51. Temperature controlled mount for beamsplitter-   52. Reflective spatial light LCD modulator-   52 a. Reflective spatial light LCD modulator-   52 b. Reflective spatial light LCD modulator-   52′. LCD modulator-   53. Individual modulator site-   54. Actuator-   55. TEC-   56. Heater-   57. Heat sink-   58. Multi-element temperature controller-   59 Single element of temperature controller-   60. Reflective or back side of spatial light modulator-   61. First modulator position-   62. Second modulator position-   63. Modulator sites-   64. Third modulator position-   65. Fourth modulator position-   67. Clear window for polarizing beamsplitter-   70. Actuator-   72. Actuator-   74. Cover glass-   74′. Cover glass-   76. Polarization compensator-   76′. LCD-   78′. Frame-   80. Black regions-   82. Clear areas-   84. First modulator position-   86. Second modulator position-   88. Third modulator position-   90. Fourth modulator position-   92. Modulator sites-   94. Non-reflecting region-   100. Printer-   132. Second lens assembly-   134. Polarizer-   142. S-polarization state of light-   144. P-polarization state of light-   150. Image plane-   151. Platen-   152. Temperature controller-   160. Photosensitive media-   184. Mask-   202. Media supply-   204. Exposure section-   206. Film processor-   208. Film storage unit-   210. Control logic processor-   212. Media handling subsystem-   220. Pellicle-   222. Integrating bar-   234. Sensor-   236. Encoding-   250. Output image-   252. Roll of media-   253. Fan

1. A method for printing an image from digital image data onto aphotosensitive medium, comprising: (a) selecting, from a set ofavailable layout formats, a selected format; (b) correlating a groupingof exposure elements on a spatial light modulator with said selectedformat; (c) modulating said grouping of exposure elements based on saiddigital image data; (d) directing an exposure beam toward said spatiallight modulator to provide an imaging beam; (e) directing said imagingbeam toward said photosensitive medium; and (f) controlling atemperature profile of said spatial light modulator.
 2. The method forprinting as in claim 1 wherein the step of selecting comprises the stepof sensing a width dimension of said photosensitive medium.
 3. Themethod for printing as in claim 1 wherein a member of said set ofavailable layout formats uses a single image.
 4. The method for printingas in claim 1 wherein a member of said set of available layout formatsuses a plurality of images.
 5. A method for printing an image fromdigital image data onto a photosensitive medium, comprising: (a)selecting, from a set of available layout formats, a selected format;(b) correlating a grouping of exposure elements on each of a pluralityof spatial light modulators with said selected format; (c) modulatingsaid grouping of exposure elements on said each of said plurality ofspatial light modulators based on said digital image data; (d) directingan exposure beam toward said spatial light modulators to provide animaging beam; (e) directing said imaging beam toward said photosensitivemedium; and (f) controlling a temperature profile of said each of saidplurality of spatial light modulators.
 6. The method for printing as inclaim 5 wherein said plurality of spatial light modulators are disposedon the same side of a beamsplitter element.
 7. The method for printingas in claim 5 wherein said plurality of spatial light modulators aredisposed on different sides of a beamsplitter element.